In recent years, there are cases where an electronic data file (simply referred to as a file, hereinafter) is stored in a file server on the Internet, and accessed from various devices (for instance, a notebook PC, a tablet-like device, a smartphone).
While the convenience of such a usage of files is high, on the other hand, there is a risk that the file may be browsed by an unintentional third party. Therefore, in a case of handling the file with high confidentiality, it is essential to take operation to secure the confidentiality using information security technology such as encryption and access restriction.
In a conventional file server, a manager manages folder configuration and also manages an access right for each folder (or each file). In addition, in a case where a file with high confidentiality is stored in the file server, after encrypting by a client, the file is transmitted to the file server, and the encrypted file is stored in the file server.
This operation prevents the file with high confidentiality from being browsed by the unintentional third party.
Patent Literatures 1 to 3 describe technique to store a confidential file in the file server. Patent Literatures 1 to 3 describe that an access right is managed for each folder and that files are encrypted and stored.